ccf 相反数

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cstdlib>
 5 #include<algorithm>
 6 using namespace std;
 7 const int maxn=1007;
 8 int num[maxn];
 9 int main()
10 {
11    // freopen("in.txt","r",stdin);
12     int n,a;int ans=0;
13     scanf("%d",&n);
14     memset(num,0,sizeof(num));
15     for(int i=1;i<=n;i++)
16     {
17         scanf("%d",&a);
18         num[a+500]++;
19     }
20     for(int i=1;i<=500;i++)
21     {
22         ans+=min(num[i+500],num[500-i]);
23     }
24     printf("%d\n",ans);
25     return 0;
26 }